The present invention relates to the field of integrated circuits and more specifically, to output buffer circuitry capable of operating at the output voltage levels needed for a particular application.
As semiconductor processing technology continues to advance, integrated circuits or “chips” continue to provide greater functionality and performance. Examples of some integrated circuits include microprocessors, application specific integrated circuits (ASICs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), and memories such as dynamic random access memories (DRAMs), static random access memories (SRAMs), and nonvolatile memories (Flash and EEPROM). The positive power supply voltage used for integrated circuits of different process technologies is often different. Generally, newer process technologies use reduced positive power supply voltages. For example, previous generation integrated circuit used a supply voltage, VDD or VCC, or 5 volts. More recent integrated circuits used 3.3- and 3-volt power supplies. Some current integrated circuits use 2.5-volt power supplies. In the future, it is expected supply voltages will be further reduced to 2 volts and lower. Some of the expected power supply voltages will be 1.2 volts, 1 volt, and 0.8 volts. Therefore, each generation of integrated circuits is compatible with a particular power supply voltage and input and output standard.
In an electronic system, it is often desirable that an integrated circuit compatible with one input-output standard can be used with integrated circuits of other input-output standards. Among the many advantages of having such a chip, the integrated circuit customer can used that particular chip on a system board with chips of other input-output standards. The integrated circuit manufacturer can produce one chip that is compatible with current and previous generation technology.
Furthermore, when there are emerging I/O standards for integrated circuits such as for a low voltage TTL (LVTTL) output or low voltage differential signal (LVDS) output, the different standards often have different voltages for VOH and VOL. Until a uniform standard is adapted, it is desirable for integrated circuit makers to design their products to be compatible with as many of the standards as possible. This will increase the overall potential market for a particular product.
Therefore, there is a need for an output circuitry that is adaptable or configurable to different I/O standards.